Blind installation of a tubular member in a workpiece is installation by access to one side only of the workpiece. One method of blind installation is the so-called pull-through method, which essentially comprises pulling an oversize mandrel head through the bore of the tubular member. In use, the tubular member is inserted in a hole in a workpiece in which the outside of the member is a fairly close radial fit. It is installed by pulling through the bore the head of a mandrel, the mandrel head having a greater external diameter than at least part of through the anvil aperture; and an enlarged head; the bore (the term "diameter" is used because the tubular bore and the mandrel head are usually both circular in cross-section, although not necessarily so). The passage of the mandrel head through the bore thus radially expands at least part of the bore and the corresponding part of the exterior of the tubular member, thereby deforming the tubular member into engagement with the workpiece in which it is inserted. The remote end of the tubular member usually protrudes from the rear face of the workpiece and is expanded to form a blind head. The mandrel is removed completely from the bore and forms no part of the installed member. Examples of such tubular members are the blind tubular rivets commercially available in many countries of the world under the Registered Trade Marks CHOBERT and BRIV.
When the head of the mandrel is pulled through a tubular member, the member must be supported axially against the axial force exerted on it by the mandrel head. This is done by means of an annular anvil, the annular face of which contacts the end of the tubular member, the mandrel stem extending through the aperture in the centre of the annular anvil. Since the tubular member is in contact with the anvil, and the mandrel head has to be pulled completely through the bore, the anvil aperture has to be of a sufficient diameter to allow the head of the mandrel to enter it and pass through it. Thus the diameter of the anvil aperture is larger than the diameter of the bore of the tubular member (or at least of that part of the bore which is radially expanded by the mandrel head).
Tubular members of the blind tubular rivet type available under the Registered Trade Marks CHOBERT and BRIV have an enlarged preformed head at one end, which head contacts the accessible face of the workpiece. In use, the tubular member is axially supported as aforesaid by contact of the anvil of the installation apparatus (usually referred to as a placing tool) with the preformed head of the member. The annular anvil can support the member by contact with the enlarged preformed head outside the workpiece, around an annular zone surrounding the anvil aperture, which zone may be spaced radially outwardly from the bore and provides no restrictions on making the anvil aperture sufficiently large to accommodate the mandrel head.
Pull-through blind installation apparatus operating in this way has been well known for many years in the art of mechanical assembly, for installing the aforementioned blind tubular rivets available under the Registered Trade Marks CHOBERT and BRIV.
In this prior art apparatus, the practice has been for a column of rivets to be loaded onto the mandrel, behind the anvil. In order to feed the next rivet along the mandrel stem to the front of the anvil, the anvil is split longitudinally into two parts along a plane containing the mandrel axis. These two parts are referred to as "jaws", since their shape and movement resemble those of a pair of jaws, although these anvil parts do not usually perform any gripping operation. When the mandrel head has been withdrawn through the anvil aperture, the column of rivets on the mandrel stem is urged forward so that the leading rivet contacts the mandrel head. The mandrel head and the leading rivet are urged forward so that they force the anvil jaws apart and allow the leading rivet through the thus enlarged anvil aperture. The anvil jaws then close behind the head of the leading rivet and around its shank, in the axial space behind that head and in front of the head of the next succeeding rivet, ready to provide axial support to the leading rivet when it is placed.
There has now arisen a requirement to install a tubular member in the form of a tubular ferrule, having no preformed enlarged head, with the nearer end of the ferrule at a distance inside the hole in the workpiece. The ferrule has a relatively thin wall, and in order to axially support the ferrule against the passage of the mandrel head as explained above, it is necessary for the anvil to support the end of the ferrule wall across substantially the full thickness thereof. Thus the anvil aperture can be no larger in diameter than the ferrule bore. Consequently the mandrel head (or at least that part of it which is of the largest diameter and which is effective to expand the ferrule) cannot pass into and through the anvil aperture. Since the anvil is inside the workpiece hole, there is no room to open the jaws as has been the practice in the prior art. Furthermore, since the tubular ferrule, when in the installation apparatus before installation, is headless and of uniform external diameter, there is no head on the leading ferrule behind which the anvil jaws could close, as described in the prior art apparatus described above. Thus it would not be possible to reliably separate the leading ferrule from the following one as the leading ferrule is fed through the anvil jaws, so that the split jaws could not be arranged to close behind the leading ferrule.
These restrictions present problems, which the present invention seeks to overcome.